State of the art methods and apparatus for inspection of an article such as a semiconductor wafer or reticle or printed circuit board (PCB) are described in the following patent documents: U.S. Pat. No. 6,816,249; U.S. Pat. No. 6,288,780; U.S. Pat. No. 5,216,479; published US Application No. 2004/0027688. The disclosures of all publications mentioned in the specification and of the publications cited therein are hereby incorporated by reference.